The present invention relates generally to automotive vehiclar heaters and more specifically to supplemental heaters for such vehicles.
At the present time automotive vehicles conventionally are supplied with heating systems which utilize heat produced by the vehicle's engine. The system includes a heater core comprising a conduit which mounts heat exchange fins. Water heated by the engine and transported through the conduit from the engine block gives up its heat through the fins to air which is caused to be passed among the fins. The heater core may, for example, be configured to fit into a rectangular passage in the order of six by eight inches positioned in a duct which passes through the fire wall separating the engine from the passenger compartment. A fan positioned upstream of the heater core is adapted to force a flow of air through the heater core and into the passenger compartment. The fan typically is provided with a selection of speeds so that an operator can vary the volume of air being directed into the passenger compartment. The air passage typically includes a path which extends directly through the heater core as well as a parallel path which bypasses the heater core with an adjustably positioned vent door (heater temperature control) provided to control the proportion of air directed through the heater.
In vehicles having relatively large engines, such as 6 or 8 cylinder engines, the heating systems are generally considered adequate, once warmed up, in providing sufficient heat to the passenger compartment. However, in vehicles having smaller engines, such as 4 cylinder engines, the engines are sometimes unable to produce enough heat to satisfactorily warm up the passenger compartment on extremely cold days. This problem is actually becoming more acute as the engines are being improved to be more efficient and therefore give up less waste heat.
Another problem presented by present day automotive heating systems is the time interval which exists between initial start up and when thermal equilibrium is eventually achieved. In some cars this may take ten or fifteen minutes or even longer depending on the particular ambient temperature involved. Since the duration of an average trip is only in the order of twenty minutes or so, much of the trip is conducted in an uncomfortable temperature condition for the operator and passengers.
Over the years various attempts have been made to deal with these problems however each has had limitations which have militated against its usefulness and general acceptance.
For example, gasoline fired heaters are available but they are bulky, expensive to provide and maintain and they are slower than desirable. Use of exhaust gas heat has been suggested but problems with eliminating any possibility of carbon monoxide gas leaking into the passenger compartment along with the relatively long warm up time required have made this approach unsatisfactory.
Electric heaters have been proposed for supplemental defrost heaters and the like but providing suitable energizing means has presented a problem which has not yet been satisfactorily solved. Typically an automobile is provided with an alternator which has a field winding adapted to be mechanically rotated by the engine to produce electric current to run the various electric loads of the vehicle. Since most of the electric loads of the car are sensitive to voltage variations a voltage regulator is provided to maintain the voltage level, within a very narrow range, at 14.4 volts (DC), suitable for most of the electric loads. The alternator is adapted to provide the voltage level despite being subjected to a wide variation of energization of the electric loads and varying mechanical input, e.g. engine speeds ranging from idle to racing. A typical large automotive alternator, operated to provide 14.4 volts, produces in the order of 1500 watts and since the electric loads normally consume 1000 or more watts, there is little power available to provide desired supplemental heat.
However an alternator can be run at a higher voltage to increase its output power. For example, it has been proposed that a deicing heater in a windshield be heated by energizing a resistive clear coating between two layers of glass. Since this requires a relatively large amount of power, the proposal entails disconnecting the alternator from the battery, then running the alternator at a higher voltage to provide sufficient power for the windshield heater and to energize the remaining electric loads in the car directly from the battery. In this system the heater can only be energized while the car is in the "PARK" position. Since the car cannot be operated while the heater is in operation this would be an unsuitable approach as a way to supplement the heater for the passenger compartment, particularly since it can only address the warm up interval and not the problems associated with continuous operation of smaller, 4 cylinder engines.
Another proposal has involved the provision of dual alternators, one operated at 14.4 volts for the normal automotive loads and the second at an elevated voltage for a supplemental heater. This, however, is not only costly initially, it is the type of component subject to wear and eventual replacement representing a significant cost item. In addition this would be relatively bulky and heavy.
Yet another problem associated with alternator powered heaters involves the selection of a heater which would work satisfactorily with the characteristics of the alternator. That is, the heater must be operable with certain widely varying varibles. For example, if used as a supplemental heater to add heat to the air stream passing through the main heater core, the heater must be capable of operating with the fan off as well as with the fan on at its maximum position (full circulation). A compromise in performance is usually required in order to avoid overheating and burn out of the heater. That is, the heater must be constructed so as to be able to generate heat without burning out with a minimum of heat dissipation when the fan is off as well as when the fan increases heat dissipation.
Voltage variations pose another problem for the selection of a heating system. For example, when the engine slows down or idles, the alternator voltage tends to drop. With a conventional wire heater having an essentially fixed electrical resistance, a change in voltage has an effect on heat produced which is dependent on the square of the voltage variation so it becomes very difficult to maintain a desirable even heat output.
It is therefore an object of the invention to provide an improvement in the performance of a heating system of an automotive vehicle. Another object is the provision of a method and apparatus to supplement the main heating system of an automotive vehicle so that the waiting time between initial energization and a thermal equilibrium for a selected temperture in the passenger compartment is significantly reduced. Another object is the provision of a method and apparatus to supplement the main heating system of an automotive vehicle which otherwise has difficulty in achieving a satisfactory comfort level in cold ambient conditions. Yet another object is the provision of a supplemental heating system which is relatively inexpensive yet extremely reliable, one which can provide even heat output even with changing voltage conditions and one which minimizes changes in currently employed automotive components and does not interfere with the normal operation of the vehicle.